Novel Hybrid Composites Based on Carbon Foams
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NOVEL HYBRID COMPOSITES BASED ON CARBON FOAMS
Joseph W. Hager* and Max L. Lake** *Wright Laboratory, WL/MLBC, Wright-Patterson AFB, OH 45433-6533
"**AppliedSciences, Inc., P.O. Box 579, Cedarville, OH 45314 ABSTRACT
The extraordinary mechanical properties of commercial carbon fiber are due to the unique graphitic morphology of the spun filaments. Contemporary advanced structural composites exploit these properties by creating a disconnected network of graphitic filaments held together by an appropriate matrix. Carbon foam derived from a blown mesophase pitch precursor can be considered to be an interconnected network of graphitic ligaments. As such interconnected networks, they represent a potential alternative reinforcing phase for structural composite materials. Based on this notion, consideration is given to novel forms of graphitic carbon and the processing routes to create hybrid composites, such as net shape fabrication and fiber placement processes. INTRODUCTION Development of fiber-reinforced composites has been driven by the need for improvements in properties such as strength, stiffness, creep resistance, and toughness in structural engineering materials. Carbon fiber reinforcements have made significant improvements in these properties in composites of various polymeric, metal and ceramic matrices. Improvement in composite properties in recent years has focussed on improved fiber properties, improved fiber/matrix interface, and increasing the fiber volume in the composite. Applications for composites have been in a wide variety of structural components, particularly for aerospace, automotive, and sports industries. Recent developments in fiber technology and the evolving need for thermal management in structures as diverse as high density electronic modules and communications satellites have stimulated research into novel reinforcements and composite processing methods.Thermal conductivity and coefficient of thermal expansion, rather than strength and elastic modulus are are the properties of paramount importance in thermal management. The new materials and requirements, combined with the continuing need to reduce the cost of composite processing warrant consideration of novel approaches. Net shape processing approaches which produce reinforced composites with minimal handling are the desired result. DISCUSSION Carbon Fiber Types Commercially available carbon fibers are continuous filaments five to fifteen microns [1]
in diameter consisting of axially aligned graphitic carbon. These fibers are manufactured by the controlled pyrolysis of spun organic polymer precursor material. Conventional high-performance carbon fibers are generally derived from either polyacrylonitrile (PAN) or mesophase pitch. PAN is the predominant precursor for high strength carbon fibers, while mesophase pitch is the predominant precursor for ultra-high modulus fibers. PAN fiber exhibits extensive cross-linking between turbostratic graphene planes. It has greater bend and compressive strength and is not as easily damaged in com
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